1. Field of the Invention
The present invention relates to a process for the preparation of copper phthalocyanine having an .alpha. polymorph. More particularly, the present invention relates to a process for the preparation of copper phthalocyanine having an .alpha. polymorph which comprises adding a dry ground mixture obtained by dry grinding crude copper phthalocyanine in the presence of a crystal growth inhibitor or a dry ground mixture obtained by dry grinding crude copper phthalocyanine in the absence of any crystal growth inhibitor and mixing the resulting dry-ground crude copper phthalocyanine with a crystal growth inhibitor to an aqueous solution of sulfuric acid to form a sulfuric acid slurry of the dry ground mixture.
2. Description of the Prior Art
A finely divided copper phthalocyanine pigment is used widely and in a large amount in the field of colorant industry because of its beautiful tone, high color strength and excellent performances such as resistance to weather and heat.
Generally, crude copper phthalocyanine is prepared by the reaction of a copper source with urea and phthalic anhydride (or a derivative thereof) or the reaction of a copper source with phthalodinitrile (or a derivative thereof) in the presence or absence of a catalyst such as ammonium molybdate or titanium tetrachloride in an organic solvent such as alkylbenzene, trichlorobenzene or nitrobenzene at a temperature of 120.degree. to 270.degree. C., preferably 170.degree. to 230.degree. C., for 2 to 15 hours, preferably 3 to 7 hours under normal or elevated pressure. However, the copper phthalocyanine molecules thus prepared cause crystal growth one after another in the solvent to give coarse acicular crystals each having a major axis of 10 to 200 .mu.m which are very lowly or no valuable as a coloring pigment for inks, coating materials or plastics.
Accordingly, the crude copper phthalocyanine thus prepared must be finely divided into particles having a high value as a coloring pigment, i.e., one having a size of about 0.01 to 0.5 .mu.m (hereinafter, this operation will be referred to as "pigmentation").
As means for the preparation of a finely divided .alpha.-type pigment of copper phthalocyanine, U.S. Pat. Nos. 3,024,247, 2,770,629 and 2,334,812 disclose an acid pasting method comprising treating crude copper phthalocyanine in a state dissolved in a large amount of concentrated sulfuric acid and an acid slurry method comprising preparing a sulfate from crude copper phthalocyanine by the use of a large amount of sulfuric acid having a concentration insufficient for dissolving the pigment therein. However, the sulfate method is particularly problematic in that the obtained pigment is poor in color strength and clarity, that the treatment time is long and that a large amount of sulfuric acid must be used, which is unfavorable in respect of waste water disposal.
As means for improving the color strength and clarity, U.S. Pat. No. 4,386,966 discloses a process for carrying out the sulfate method in the absence of any crystal growth inhibitor. However, this process is also problematic in that the obtained pigment is poor in color strength, transparency or weathering resistance depending upon the conditions of the pigmentation, that copper phthalocyanine having a .gamma. polymorph which causes significant bronzing is formed as a by-product and that the crude copper phthalocyanine to be used is limited to semi-chloro copper phthalocyanine, because remarkable crystal growth occurs when chlorine-free copper phthalocyanine is used.